CVE-2021-34527 PoC — Windows Print Spooler Remote Code Execution Vulnerability

Source

https://github.com/DenizSe/CVE-2021-34527

Associated Vulnerability

Title: Windows Print Spooler Remote Code Execution Vulnerability (CVE-2021-34527)
Description:A remote code execution vulnerability exists when the Windows Print Spooler service improperly performs privileged file operations. An attacker who successfully exploited this vulnerability could run arbitrary code with SYSTEM privileges. An attacker could then install programs; view, change, or delete data; or create new accounts with full user rights. UPDATE July 7, 2021: The security update for Windows Server 2012, Windows Server 2016 and Windows 10, Version 1607 have been released. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. If you are unable to install these updates, see the FAQ and Workaround sections in this CVE for information on how to help protect your system from this vulnerability. In addition to installing the updates, in order to secure your system, you must confirm that the following registry settings are set to 0 (zero) or are not defined (Note: These registry keys do not exist by default, and therefore are already at the secure setting.), also that your Group Policy setting are correct (see FAQ): HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows NT\Printers\PointAndPrint NoWarningNoElevationOnInstall = 0 (DWORD) or not defined (default setting) UpdatePromptSettings = 0 (DWORD) or not defined (default setting) Having NoWarningNoElevationOnInstall set to 1 makes your system vulnerable by design. UPDATE July 6, 2021: Microsoft has completed the investigation and has released security updates to address this vulnerability. Please see the Security Updates table for the applicable update for your system. We recommend that you install these updates immediately. If you are unable to install these updates, see the FAQ and Workaround sections in this CVE for information on how to help protect your system from this vulnerability. See also KB5005010: Restricting installation of new printer drivers after applying the July 6, 2021 updates. Note that the security updates released on and after July 6, 2021 contain protections for CVE-2021-1675 and the additional remote code execution exploit in the Windows Print Spooler service known as “PrintNightmare”, documented in CVE-2021-34527.

Description

Small Powershell Script to detect Running Printer Spoolers on Domain Controller

Readme

# CVE-2021-1675 / CVE-2021-34527

Two mini Script to check if the PrintSpooler Serivce is running within the Forest.

CVE-2021-1675:

https://msrc.microsoft.com/update-guide/en-US/vulnerability/CVE-2021-1675

CVE-2021-34527 aka PrintNightmare

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2021-34527

## Scripts

Detect running Printer Spooler Service on DCs:

https://github.com/DenizSe/CVE-2021-1675/blob/main/Get-PrinterSpoolerState.ps1

Detect running Printer Spooler Service on Machines within OU:

https://github.com/DenizSe/CVE-2021-1675/blob/main/Get-PrinterSpoolerStateOU.ps1

# Official Guidance (Taken from CVE-2021-34527

## Workarounds
Determine if the Print Spooler service is running (run as a Domain Admin)

Run the following as a Domain Admin:

Get-Service -Name Spooler

If the Print Spooler is running or if the service is not set to disabled, select one of the following options to either disable the Print Spooler service, or to Disable inbound remote printing through Group Policy:

### Option 1 - Disable the Print Spooler service

If disabling the Print Spooler service is appropriate for your enterprise, use the following PowerShell commands:

Stop-Service -Name Spooler -Force

Set-Service -Name Spooler -StartupType Disabled

Impact of workaround Disabling the Print Spooler service disables the ability to print both locally and remotely.

### Option 2 - Disable inbound remote printing through Group Policy

You can also configure the settings via Group Policy as follows:

Computer Configuration / Administrative Templates / Printers

Disable the “Allow Print Spooler to accept client connections:” policy to block remote attacks.

Impact of workaround This policy will block the remote attack vector by preventing inbound remote printing operations. The system will no longer function as a print server, but local printing to a directly attached device will still be possible.

For more information see: Use Group Policy settings to control printers.

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